This time round, the scientists found nothing along the first 250 or so kilometres (155 miles) of the survey area. But in the next 250 kilometres, they found three new vents, including one of the strongest the team has ever studied.

"It was very, very strong - so that will be a bit intriguing to finally get down there with a camera," said Dr Cornel de Ronde, a marine geologist with New Zealand's Institute of Geological and Nuclear Sciences.

At another undersea volcano, the scientists dredged up rocks, which "when we hit them with a hammer onboard, the rock would break open and all this incredible steam would come out of them.

"So, we just measured it with a thermometer for a laugh. It was 57 Celsius. Definitely hot rocks," said Dr de Ronde.

Hit and miss

Finding the third new hydrothermal field was a matter of luck.

"Inadvertently, when the position got given to the captain, we swapped around a couple of numbers so the survey started about two kilometres south of the volcano," the marine geologist said.

The survey team wants to know why some areas are more active than others

"We had to go up over this little knoll, and lo and behold, it was just absolutely ripping with hydrothermal vents. So it was a bit of serendipity there."

Dr de Ronde is now pondering why long stretches of the Kermadec Arc are hydrothermally active while others are not.

"It's as if parts of the arc are switched on and other parts are switched off. It would seem that magma and heat from the boundary between the Australian and Pacific plates reaches the Earth's crust in some places and not in others."

Other scientists from other disciplines - the team included New Zealand, American and Japanese scientists - also have intriguing material to study.

Hot, hot, hot

The scientists brought home a mix of animals that appear to thrive in the hot volcanic plumes. "There is absolutely sensational material," said marine biologist Dr Steve O'Shea, from New Zealand's National Institute of Water and Atmospheric Research (NIWA).

Included in the haul are a brand new bivalve and two new species of mussel.

Some of the submarine volcanoes are truly massive

"It's just so novel that I shouldn't even say anything because you don't know what this stuff is until you've sat down and looked at it for months and months," he added.

Microbiologists, too, were also able to recover microbes from seawater in the black smoker plumes and grow them at 70 C in laboratory conditions on board the New Zealand research ship.